E-Z Isomerization and aggregation phenomena of dithiafulvenes in CHCl3. , , and . ., 2009, 74, 2114–2119

ALEJANDRO M FRACAROLI; ALEJANDRO M. GRANADOS; RITA H. DE ROSSI

JOURNAL OF ORGANIC CHEMISTRY

Merican Chemical Society

Lugar: Washington; Año: 2009 vol. 74 p. 2114 - 2119

0022-3263

The physical-chemical properties of several 1,3-dithiafulvene (DTF) derivatives having a donor andacceptor group in the molecule were studied. The synthesis of these compounds produces selectively theE isomer, but when the compound is dissolved in CHCl3 isomerization to the Z isomer takes place witha rate that depends on the substituents. The interconversion rate is slow on the NMR time scale; therefore,two separated signals are observed, and they are used to measure the rate constant of isomerization. Theequilibrium constant is, in all cases, very close to 1, and this is coincident with the fact that theoreticalcalculations of the energy of the two isomers in the gas phase differ by less than 0.1 kcal/mol. Theisomerization reaction is completely reversible, and the E isomer can be obtained in pure form by selectivecrystallization. The derivatives with thioalkyl groups have a strong tendency to aggregate in CDCl3. Theformation of the aggregates is evidenced from the changes in 1D 1H NMR and DOSY spectra as afunction of concentration. The compounds are highly delocalized, and this is reflected by the low activationenergy for the isomerization.